A light emitting diode is a device that converts electrical energy into light energy. When a forward voltage is applied to a light emitting diode including an n-type semiconductor layer and a p-type semiconductor layer, electrons from the n-type semiconductor layer combine with holes from the p-type semiconductor layer, and as a result, energy corresponding to the band gap energy between the conduction band and the valence band is usually released in the form of heat or light.
Various types of compound semiconductors are used in the fabrication of light emitting diodes that produce various colors. Particularly, nitride semiconductors are extensively used in the field of photonic device and high power electronic device development due to their good thermal stability and wide band gap energy.
Commercial light emitting diodes using nitride semiconductors are now widely used. Such light emitting diodes include blue light emitting diodes, green light emitting diodes, and ultraviolet (UV) light emitting diodes. With the recent increasing demand for highly efficient LEDs, an improvement in luminous efficiency is emerging as a major issue.